The present invention generally relates to surveillance systems which capture and store visual information generated by one or more surveillance cameras, and more particularly to an improved recording arrangement allowing such systems to be triggered by occurrence of a particular event while still recording the entire event.
Surveillance systems which record images from one or more video cameras or closed circuit televisions systems are well known in the art. These systems allow time sequential visual records to be stored as analog signals on videotape or digital images in a personal computer (PC) memory device for later review and analysis. A common problem for all such systems is balancing the availability of a finite amount of physical space for storage of captured signals with the potentially large amount of information which may need to be recorded in carrying out continual surveillance over long periods of time. One known approach for addressing this problem involves only activating image recording in response to specific triggering events, such as opening of a door, operation of a cash register or ATM, or tripping of a sensor. By triggering recording only when particular events occur, such arrangements not only significantly reduce the amount of video information to be recorded, but also assure the images that are stored have the highest probability of being of interest.
While such event triggered systems effectively eliminate the need for large information storage space, the requirement that recording does not begin until after occurrence of one of the events insures that the period of time just preceding the event will never be recorded. Unfortunately, it is this preceding period of time which tends to be of greatest interest when later analyzing the recorded information. Therefore, a need exists for an improved surveillance system capable of reducing the need for the large storage space without reducing the system""s capability to record information likely to be the most useful.
Therefore, it is an object of the present invention to provide a surveillance and image capture system and method which overcomes the above-noted problems by constantly recording surveillance information into temporary and reusable storage, and recording such information for long-term storage and subsequent retrieval upon the occurrence of multiple and overlapping predefined triggering events.
It is another object of the present invention to provide a digital image recording arrangement for use in a surveillance system which continuously records digital image data from multiple video sources into a cache memory to create a pre-event image data store, and subsequently stores the pre-event digital image data in proper time sequential order from each of the multiple video sources into long-term data storage for later retrieval and analysis upon the occurrence of one or more overlapping triggering events from any one or all of the video sources.
It is yet another object of the present invention to provide a digital image recording arrangement for use in a surveillance system which is capable of true pre-event image recording for systems having multiple image input sources.
In accordance with these and other objects of the present invention, pre-event recording is achieved by providing an image recording system for use with a surveillance system having at least two cameras, wherein the recording system includes a processor connected to the at least two video cameras for receiving generated video images and image creation time identifying information, a temporary storage device connected to the processor and having a storage capacity large enough to store video images generated over a predetermined period of time, a long-term storage device also connected to the processor, and a sensor arrangement for detecting an occurrence of a pre-defined triggering event associated with each camera. The processor is arranged to continuously record video images from each camera into the temporary storage device, and in response to the sensor arrangement detecting the occurrence of a triggering event associated with any of the at least two cameras, subsequently record temporarily stored video images generated by the associated camera into the long term storage device.
In accordance with one aspect of the present invention, the sensor arrangement is arranged to detect an occurrence of overlapping pre-defined triggering events, and the image recording processor is further arranged to subsequently record the temporarily stored video images generated by each camera associated with the detected triggering events into the long-term storage device. The image recording processor is further arranged to detect that images from an earlier triggering event but occurring after a starting time for a later triggering event have been recorded into the long-term storage device, and in response, automatically altering the sequence of images recorded to the long-term storage device to place the images associated with each overlapping triggering event in a combined oldest to latest time sequence.
In accordance with another aspect of the present invention, a method for recording video images in a surveillance system having at least two cameras includes receiving video images generated by the at least two video cameras and determining an image creation time for each received image, and recording the received video images in a temporary storage device having a storage capacity large enough to store video images generated over a predetermined period of time. Upon detecting an occurrence of a pre-defined triggering event associated with one of the cameras, the temporarily stored video images generated by the associated camera into a long-term storage device while continuing to maintain any images recorded in the temporary storage device generated by any camera not associated with triggering event.
In accordance with still another aspect of the present invention, the method detects an occurrence of overlapping pre-defined triggering events associated with different cameras, and in response to each triggering event, subsequently records temporarily stored video images generated by each camera associated with the detected triggering events into a long-term storage device. In addition, upon detecting that images from an earlier triggering event but occurring after a starting time for a later occurring triggering event have been recorded into the long-term storage device, the sequence of images recorded to the long-term storage device is automatically altered to place the images associated with each overlapping triggering event in a combined oldest to latest time sequence.
In accordance with other aspects of the present invention, the received video images are captured as digital image data and compressed before recording in the temporary storage device. The temporary storage device can be implemented as a cache memory, and the oldest video images in the temporary storage device are automatically overwritten when the storage capacity is filled.
Thus, the present invention provides a true pre-event recording arrangement for multiple video input sources that is further capable of handling the occurrence of overlapping triggering events by automatically xe2x80x9crewindingxe2x80x9d the sequential long term storage process so that any images associated with an earlier triggering event but occurring in time after a later triggering event that have already been stored to long term storage are properly reordered to occur after any earlier occurring images associated with the later triggering event.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.